Electrosurgery is the delivery of radio-frequency (RF) current through body tissue to raise tissue temperature for cutting, coagulating, and desiccating. With its first use dating back almost a century, electrosurgery has become common surgical practice.
In a typical application, electrical current is applied to preselected tissue using a unipolar electrode. The customary unipolar electrode consists of a stainless steel shaft or similar substrate that is substantially coated on its outer surface with an insulative (i.e., electrically nonconductive) coating. One end of the substrate is exposed for tissue contact.
During surgery, a return electrode is attached to the patient at a position away from the surgical area. A generator is then used to energize the electrode substrate. The exposed end of the electrode is brought into contact with preselected tissue of a patient which results in a current path being provided between the electrode and the patient. Current from the electrode develops a high temperature region about the electrode's exposed end which destroys tissue.
Coinciding with the rise in minimally invasive surgical procedures, recent development efforts in electrosurgery have principally centered on instruments suitable for closed procedures such as laparoscopy and endoscopy. Reflecting these efforts are the wide variety of specialized surgical electrodes now available. Examples include electrodes with a spatula tip, sling tip, scissor tip, forcep tip, cone tip, and button tip.
Somewhat left behind in these advancements has been the electrosurgical blade, or scalpel. Although they are used in the more traditional open surgical techniques, electrosurgical blades have in many respects more exacting performance requirements than electrodes used in closed procedures. The performance requirements for electrosurgical blades are more exacting because surgeons call upon these instruments to handle like a traditional scalpel.
A persistent problem with all surgical electrodes, especially noticeable and problematic for blade-style electrodes, is tissue sticking. Specifically, the electrosurgery causes charred tissue, commonly called "eschar," to adhere to the working surface of the electrode. For electrosurgical blades, the effect on handling from such stuck tissue mimics that of a dulled blade.
Numerous methods exist for providing a non-stick surface or coating to electrosurgical instruments. Unfortunately, the conventional non-stick coatings are also electrically insulative and therefore, not suitable for the working surface of electrosurgical blades.
Efforts at developing a conductive non-stick working surface for electrosurgical blades are the subject of other patents. For example, U.S. Pat. No. 4,785,807 to Blanch is directed to a stainless steel blade electrode completely covered by a coating of fluorinated hydrocarbon that is so thin it allows some conduction of radio-frequency electrical energy. This thin coating approach has at least two serious drawbacks. First, such thin coatings are not wear resistant and therefore, soon lose their non-stick effect. Second, it relies upon a capacitive coupling across the coating, a phenomena which both limits energy delivery and prevents uniform distribution of that energy.
There continues to be a need for improved electrosurgical blades that are durable yet surgeon friendly. In particular, there remains a need for an electrosurgical blade that overcomes the tissue sticking problem, without a corresponding drop in effectiveness for other performance criteria such as coagulation efficacy. To this end, it has now been found that the temperature profile transversely across the blade, i.e. between opposed cutting edges, is an important factor for optimizing blade performance.